Power tool motors can generally be grouped into two categories: brushed motors and brushless motors. In a brushed motor, motor brushes make and break electrical connection to the motor due to rotation of the rotor. In a brushless motor power tool, such as power tool 100 of FIG. 1, switching elements are selectively enabled and disabled by control signals from a controller to selectively apply power from a power source to drive the brushless motor. The power tool 100 is a brushless hammer drill having a housing 102 with a handle portion 104 and motor housing portion 106. The power tool 100 further includes an output unit 107, torque setting dial 108, forward/reverse selector 110, trigger 112, battery interface 114, and light 116.
FIG. 2 illustrates a simplified block diagram 120 of the brushless power tool 100, which includes a power source 122 (e.g., a battery pack), Field Effect Transistors (FETs) 124, a motor 126, hall sensors 128, a motor control unit 130, user input 132, and other components 133 (battery pack fuel gauge, work lights (LEDs), current/voltage sensors, etc.). The Hall sensors 128 provide motor information feedback, such as motor rotational position information, which can be used by the motor control unit 130 to determine motor position, velocity, and/or acceleration. The motor control unit 130 receives user controls from user input 132, such as by depressing the trigger 112 or shifting the forward/reverse selector 110. In response to the motor information feedback and user controls, the motor control unit 130 transmits control signals to accurately control the FETs 124 to drive the motor 126. By selectively enabling and disabling the FETs 124, power from the power source 122 is selectively applied to the motor 126 to cause rotation of a rotor. Although not shown, the motor control unit 130 and other components of the power tool 100 are electrically coupled to the power source 122 such that the power source 122 provides power thereto.